$> pip install --upgrade GitPython
Collecting GitPython
  Downloading GitPython-2.1.3-py2.py3-none-any.whl (442kB)
Requirement already up-to-date: gitdb2>=2.0.0 in /home/yoh/proj/datalad/datalad/venv-tests/lib/python2.7/site-packages (from GitPython)
Requirement already up-to-date: smmap2>=2.0.0 in /home/yoh/proj/datalad/datalad/venv-tests/lib/python2.7/site-packages (from gitdb2>=2.0.0->GitPython)
Installing collected packages: GitPython
  Found existing installation: GitPython 2.1.0
    Uninstalling GitPython-2.1.0:
      Successfully uninstalled GitPython-2.1.0
Successfully installed GitPython-2.1.3
You are using pip version 7.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

$> python -c 'from git import Repo; print Repo(".").submodules'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/yoh/proj/datalad/datalad/venv-tests/local/lib/python2.7/site-packages/git/repo/base.py", line 290, in submodules
    return Submodule.list_items(self)
  File "/home/yoh/proj/datalad/datalad/venv-tests/local/lib/python2.7/site-packages/git/util.py", line 932, in list_items
    out_list.extend(cls.iter_items(repo, *args, **kwargs))
  File "/home/yoh/proj/datalad/datalad/venv-tests/local/lib/python2.7/site-packages/git/objects/submodule/base.py", line 1181, in iter_items
    sm = rt[p]
  File "/home/yoh/proj/datalad/datalad/venv-tests/local/lib/python2.7/site-packages/git/objects/tree.py", line 293, in __getitem__
    info = self._cache[item]
IndexError: list index out of range

$> git submodule
+60d265e09441a6316f7c3336c0eba4370afed2ac 2009 (heads/master)
+5cdff4402dec87be62ae0ba197c63ad1da7ba2c2 2010 (heads/master)
+e5638100b6e4514a6e6e7379a581fb2801b7a59b 2011 (heads/master)
+62bf8ad207a8d70706a3b1288e2aaa6b1efe20ed 2013 (heads/master)
+214a854c94d9d8c5283643a59fb633f46563fbd0 2014 (heads/master)
+a6770f5aa5c8552b3cd803b138e5ae71c281188b 2015 (heads/master)
+4790ba30c6e666c86ec26d78042eb2a82cb043f8 2016 (heads/master)
+bf191a0120bce11be84f3e9a260eb830939fecbc 2017 (heads/master)

$> git diff
diff --git a/2009 b/2009
index b547198..60d265e 160000
--- a/2009
+++ b/2009
@@ -1 +1 @@
-Subproject commit b547198f5c417a88fa3e683c7a73b2ba014b2331
+Subproject commit 60d265e09441a6316f7c3336c0eba4370afed2ac
...

$> head .gitmodules 
[submodule "2009"]
	path = 2009
	url = ./2009
[submodule "2010"]
	path = 2010
	url = ./2010
[submodule "2011"]
	path = 2011
	url = ./2011

$> rm -rf /tmp/test && mkdir /tmp/test && cd /tmp/test; git init; echo smth > smth; git add smth; git commit -m smth; mkdir sub; cd sub; git init; echo 123 > 123; git add 123; git commit -m added ; cd ../; git submodule add ./sub sub; cd sub; echo 124 >| 123; git add 123; git commit -m changed; cd ..; git submodule; python -c 'from git import Repo; print Repo(".").submodules'
Initialized empty Git repository in /tmp/test/.git/
[master (root-commit) bbfc6e1] smth
 1 file changed, 1 insertion(+)
 create mode 100644 smth
Initialized empty Git repository in /tmp/test/sub/.git/
[master (root-commit) 6063d92] added
 1 file changed, 1 insertion(+)
 create mode 100644 123
smth  sub/
Adding existing repo at 'sub' to the index
123
[master 4a3e397] changed
 1 file changed, 1 insertion(+), 1 deletion(-)
smth  sub/
+4a3e397542e87ff842555f8f6c6fdfafffa0c375 sub (heads/master)
[git.Submodule(name=sub, path=sub, url=./sub, branch_path=refs/heads/master)]
changes on filesystem:                                                                                                                                                                                                                       
 sub | 2 +-
cached/staged changes:
 .gitmodules | 3 +++
 sub         | 1 +